Argh but it has nothing to do with being lazy
But we are in this hobby to create sustainability and try to mimic nature as best as possible by providing a non fluctuating enviromant
Controllers are intuitive making your system run in step with nature by allowing things such as accurate dosing, sustaining pH levels, salinity levels to be kept in check all able to sync together (talk to each other)
Seperates can not talk to each other, for instance GHL salinity control programmed together with auto top off to make sure your salinity does not fluctuate. Thats just one important example where controllers come up above seperates, the ability to combine important functions that your system requires for stability.
Many functions a tank needs interlock with each other seperate controllers like ph and levels can not do.
Another example. tunze control timed and sync'd with moon phase of your lighting for nocturnal ebb and flow.
Level sensor alarms that turn off pumps incase off floods.
I could go on, but this has to be the biggest advantage over seperates that any controller has.